Investigation of Infrared Photo-Detection Through Subgap Density-of-States in a-InGaZnO Thin-Film Transistors

Amorphous InGaZnO (a-IGZO) thin-film transistors (TFTs) are investigated for a possible application to infrared (IR) photodetector through subgap density-of-states over the forbidden bandgap. The origin of the sub-bandgap( ${h}\nu < {E} _{g})$ photo-response in a-IGZO TFTs is due to optically pumped electrons from the photo-responsive subgap states ( ${E} _{C}$ - ${E} _{\textit {ph}}{<}{E}_{t}{<}{E}_{F})$ . Among the sub-bandgap lights, we investigate the reproducible IR photo-response in a-IGZO TFTs as a photodetector without the persistent photoconductivity (PPC) effect. In this letter, we characterize the IR photo-response mechanism through various optical and electrical measurements on the wavelength, optical power, bias-modulated quasi-Fermi level, and photo-responsive states. This result is expected to provide independent and/or integrated IR detector with transparent substrate combined with a-IGZO TFTs.